Capacitors such as decoupling capacitors on semiconductor devices are essential components used to filter noise that may be present between operating supplies such as power and ground. Some semiconductor fabrication processes construct decoupling capacitors on a silicon substrate by forming one electrode into the substrate itself and then forming a second electrode from an overlying conductive material with the two electrodes being separated by a dielectric material. Various capacitors and methods for forming capacitors such as decoupling capacitors, both on a semiconductor chip and on a printed circuit board, are described in the following U.S. patents each assigned to Micron Technology, Inc., each of which is incorporated herein by reference: U.S. Pat. No. 4,879,631 issued Nov. 7, 1989 to Johnson et al.; U.S. Pat. No. 5,032,892 issued Jul. 16, 1991 to Chern et al.; U.S. Pat. No. 5,155,656 issued Oct. 13, 1992 to Narashimhan et al.; U.S. Pat. No. 5,304,506 issued Apr. 19, 1994 to Porter et al.; U.S. Pat. No. 5,266,821 issued Nov. 30, 1993 to Chern et al.; U.S. Pat. No. 5,329,237 issued Jul. 12, 1994 to Horch.
The formation of capacitors over the surface of a semiconductor can leave the substrate and capacitor dielectric susceptible to subsequent process steps such as future dopant implants that can penetrate into the silicon substrate and thereby short the two capacitor plates together through the capacitor dielectric. Also, subsequent plasma etches can further damage the capacitor by reducing the overall surface area of the second electrode if it is not protected.
An improved capacitor and fabrication process therefor which reduces the problems associated with some other capacitors and methods of capacitor formation would be desirable.